Posted by **American Public University** on Saturday, May 4, 2013 at 4:47pm.

the percent defective for parts produced by a manufacturing process is targeted at 4%. The process is monitored daily by taking samples of sizes n=160 units. Suppose that today's sample contains 14 defectives. How many units would have to be sampled to be 95% confident that you can estimate the fraction of defective parts within 2% (using the information from today's sample-that is using the result that P=0.00875)?

- statistics -
**MathGuru**, Sunday, May 5, 2013 at 6:26pm
Formula to find sample size:

n = [(z-value)^2 * p * q]/E^2

... where n = sample size, z-value is found using a z-table for 95% confidence (which is 1.96), p = .0875, q = 1 - p, ^2 means squared, * means to multiply, and E = .02.

Plug values into the formula and calculate n. Round the answer to the next highest whole number.

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**Robert**, Sunday, January 4, 2015 at 11:33pm
After calculating the sample size needed to estimate a population proportion to within 0.05, you have been told that the maximum allowable error (E) must be reduced to just 0.025. If the original calculation led to a sample size of 1000, the sample size will now have to be .

- statistics -
**Robert**, Sunday, March 8, 2015 at 7:07am
4000

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